Archaean subduction

Re-Os studies of mantle nodules demonstrate that the craton keel is Archaean in age and that there is no correlation with depth in the keel. The keel, therefore, did not thicken over time. Many eclogite inclusions in diamond are the same age as depleted peridotite or even slightly older. The age data on eclogite inclusions, coupled with evidence from stable isotope measurements that the eclogites formed from seawater-altered basalts, indicate that subduction processes were probably important in Archaean... 

Richardson, S. H., Shirey, S. B., Harris, J. W. Carlson, R. W. 2001. Archaean subduction recorded by Re-Os isotopes in sulphide inclusions in diamonds. Earth and Planetary Science Letters, 191, 239-248. 

Martin, H. 1986. Effect of steeper Archaean geothermal gradient on geochemistry of subduction-zone magmas. Geology, 14, 753-756. 

Calvert, A. J., Sawyer, E. W., Davis, W. J. Lud-DEN, J. N. 1995. Archaean subduction inferred from seismic images of a mantle suture in the Superior Province. Nature, 375, 670-674. 

White, D. J., Mussachio, G., Sol, S. Lithoprobe Western Superior Working Group 2001. Evidence for subduction processes and terrane accretion in the Archean Western Superior Province, Canada results from combined LITHOPROBE deep seismic studies. In Cassidy, K. F., Dunphy, J. M. VAN Kranendonk, M. J. (eds) 4th International Archaean Symposium, 24-28 September 2001, Extended Abstracts. AGSO-Geoscience Australia, Record, 2001/37, 539. 

Fig. 14. Fluxes of CO2 are shown as functions of time for the high heat-flow models in Figures 12 and 13. Impact ejecta are of minor importance compared with the rapid churning of the oceanic crust. In Archaean time, CO2 is mostly controlled by processes involving the creation and subduction of oceanic crust. Continents become increasingly important through Proterozoic time, with the transition from mantle to continental control occurring at c. 1.4 Ga.

One particular class of Archaean mantle xenoliths has received special attention. These are eclogites recovered from the subcontinental lithosphere. Richardson et al. (2001) showed that some Archaean eclogite xenoliths have the trace element and Os-isotopic characteristics of a basaltic protolith and an isotopic history which shows a significant time gap between basalt generation and eclogite crystallization. These properties are typical of subducted ocean floor and indicate that the subcontinental lithosphere beneath the Kaapvaal Craton contains fragments of 2.9 Ga subducted ocean floor. 

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